This invention relates to a combined differential gear device including a first differential gear mechanism and a second differential gear mechanism which is built in the first differential gear mechanism.
Heretofore, there has been known one, as a differential gear device of this type, which is disclosed in Japanese Patent Application Laid-Open No. H10-220556, for example. The combined differential gear device disclosed in this Laid-Open publication comprises a housing (input member) driven for rotation, at least a pair of planetary gears disposed within this housing in parallel with an axis of the housing such that they can rotate about their own axes, and a pair of side gears (output members) rotatably disposed within the housing with their axes aligned with the axis of the housing. The pair of planetary gears are in meshing engagement with each other and also in meshing engagement with the pair of side gears, respectively. The first differential gear mechanism is constituted by the housing, the pair of planetary gears and the pair of side gears. A rotary torque input into the housing is distributed to the pair of side gears through the pair of planetary gears.
One of the pair of side gears is provided with a casing of the second differential gear mechanism such that the casing can rotate in unison with the side gear. This casing is provided therein with a pinion gear constituted by a bevel gear whose axis is orthogonal to an axis of the casing and a pair of second side gears whose axes are aligned with the axis of the casing. The pinion gear and the second side gears are rotatably supported on the casing and meshed with each other. Accordingly, the rotary torque distributed to the above-mentioned one of the pair of side gears is further distributed to the pair of second side gears. The rotary torque distributed to one of the second side gears is transmitted, for example, to one of the left and right front wheels or one of the left and right rear wheels. On the other hand, the rotary torque distributed to the other side gear is transmitted to a rear differential gear device in case the combined differential gear device is used as a center and front differential gear device, and transmitted to a front differential gear device in case the combined differential gear device is used as a center and rear differential gear device. Then, the rotary torque is transmitted from the rear or front differential gear device to the left and right rear wheels or the left and right front wheels.
In a vehicle equipped with a combined differential gear device thus constructed, it is demanded that the rotary torque transmitted to the front wheels is different in magnitude from the rotary torque transmitted to the rear wheels. In such a case, it is required to increase the ratio of the rotary torque, i.e., torque bias ratio, transmitted to the pair of side gears as output members. However, in the conventional combined differential gear device, in order to increase the torque bias ratio between the pair of side gears, attention is paid only to the side gears and the planetary gears of the first gear mechanism but no attention is paid to the second gear mechanism at all. For this reason, there is such a problem that the torque bias ratio is difficult to be more increased.
The present invention has been accomplished in order to solve the above-mentioned problem. The features of the present invention reside in a combined differential gear device comprising a first differential gear mechanism including an input member driven for rotation, a pair of output members rotated by the input member through at least one planetary gear and a housing containing therein the input member and the pair of output members; and a second differential gear mechanism including a casing disposed within the housing, a pinion gear rotatably disposed within the casing and a pair of side gears rotatably disposed within the casing with their axes aligned with each other and meshed with the pinion gear; wherein the casing is divided into plural parts in a direction of the axes of the pair of side gears, one part of such divided parts, which supports the pinion gear, being rotatably disposed at the housing and non-rotatably connected to one of the pair of output members; another part of the divided parts, which supports one of the pair of side gears, being movable in a direction of the axes of the pair of side gears.
It is preferred that the casing is divided into three parts including an intermediate part which supports the pinion gear, and a pair of side parts which support the pair of side gears, respectively, the intermediate part is rotatably disposed with respect to the housing and non-rotatably connected to one of the pair of output members, and one of the pair of side portions is movable in the direction of the axes of the side gears. Especially, it is preferred that a part of the housing also serves as the other of the pair of side portions.
It is also preferred that the casing is divided into two parts including a part which supports the pinion gear and one of the pair of side gears and a part which supports the other side gear, the part, which supports the pinion gear and one of the pair of side gears, is movable in the direction of the axes of the pair of side gears, and a part of the housing also serves as the part which supports the other side gear.
It is accepted that the first differential gear mechanism includes an inner gear, a carrier and a sun gear whose axes are all aligned with one another, and at least one planetary gear rotatably disposed at the carrier and meshed with the inner gear and the sun gear, any one of the inner gear, the carrier and the sun gear serves as the input member, and the remaining two serve as the output members.